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利用密度泛函理论的平面波赝势方法研究了IrTi合金的晶格动力学行为.声子谱计算表明四方(L10)结构动力学不稳定,通过冷冻不稳定声子模式,发现IrTi会发生从四方(Ll_0)到正交的结构相变.进一步分析软模对应的原子振动,得到了具有正交对称性,空间群为Cmmm,相对于四方(Ll_0)相能量更低、更稳定的结构.这种正交新相(Cmmm)弹性稳定和动力学稳定,而且其结构参数与实验上观察到的低温结构有限的晶格参数相符合,表明IrTi合金的低温相是正交结构(Cmmm).从理论上肯定了IrTi合金立方到四方再到正交的相变机制,解决了实验上关于相变机制和低温相结构形式的争议.
The crystal lattice dynamics of IrTi alloy has been studied by density functional theory (PFT) method. The phonon spectra show that the tetragonal (L10) structure is unstable. By means of the frozen unstable phonon model, (Ll_0) to the orthogonal structural phase transitions, the atomic vibrations corresponding to the soft modes are further analyzed, and the structure with orthogonal symmetry, space group Cmmm, lower and more stable energy than the quadrilateral (Ll_0) phase is obtained. The new orthorhombic new phase (Cmmm) is elastic and dynamic, and its structural parameters agree well with the experimentally observed lattice parameters of low temperature structure, indicating that the low temperature phase of IrTi alloy is orthogonal structure (Cmmm). From Theoretically, the phase transition mechanism from cubic to tetragon of IrTi alloy to quadrature is confirmed, and the controversy about the phase transition mechanism and the structure of low temperature phase in experiment is solved.